Hi Mike, The following segfaults on Mac OS X 10.7.4 running on Intel Core i5. Reverting to 2139c6791f4b802560ce62dc688293786803a9ca makes it happy again. Not sure if this is a bug or some caveat I've missed regarding "FFI: Box all accessed or returned enums." local ffi = require "ffi" ffi.cdef[[ int socket(int domain, int type, int protocol); ]] local sock = ffi.C.socket(2, 1, 6) print("SOCK:", sock) -- doesn't get here Any tips would be great. Thanks! Richard